Coated sliding material

ABSTRACT

In order to prevent the cracking of a coating of sliding material, in which an electroless Ni-B plating coating layer is formed on the surface of aluminum alloy, an electroless Ni-P plating coating layer is provided on the aluminum alloy.

TECHNICAL FIELD

The present invention relates to sliding material. More particularly,the present invention relates to sliding material used for the substrateof such sliding members as the vane, scroll, piston and the like of acooler-compressor, said substrate consisting of aluminum-alloy beingsubjected to surface treatment.

PRIOR ART

It is known that the aluminum-alloy is used for the above describedsliding material to reduce weight, and, further, surface treatment iscarried out for enhancing its sliding properties.

As a prior art of surface treatment for enhancing the seizure-resistanceof a scroll made of aluminum-alloy, Japanese Unexamined PatentPublication No. Sho 62-199,982 refers to electroless Ni plating, ceramicdispersion-plating, ceramic flame-plating and the like, as prior art.Allegedly, the electroless Ni-B plating is superior to these prior artsbecause of good wear-resistance and distribution of coating thickness.

Japanese Unexamined Patent Publication No. Sho 58-193,355, which belongsto a prior art of the surface treatment, is related to the platingmethod in which the electroless Ni-P plating is applied on the surfaceof a work piece made of steel and, subsequently, electroless compositeplating is carried out with co-deposition of ultra-hard fine particles.It teaches that flash plating by the electroless Ni-P plating acts as aprecursor of the composite plating and improves the throwing power ofthe plating.

In addition, Japanese Examined Patent Publication No. Hei 2-50,993 isrelated to the improvement of corrosion-resistance of coating, in whichan Ni-W-P plating layer is formed on an Ni-P plating layer. Allegedly,no drawbacks of each of these plating layers appear, but, the coatingprovided exhibits improved corrosion-resistance, hardness,wear-resistance, and resistance to embrittlement, when these layers areused in a combination.

Since the hardness of Ni-B plating is in the range of Hv=700˜900, whilethe hardness of aluminum alloy is in the range of Hv=100˜140, thedifference in hardness between the plating coating and thealuminum-alloy, which is a substrate, is very great. In addition, sincethe internal tensional stress acts on the Ni-B plating coating, peelingis likely to occur. Because of this property of the Ni-B platingcoating, when the Ni-B plating coating is directly applied on thesurface of aluminum alloy, and is exposed to the reciprocating load orimpact force from the opposite material, chipping or peeling is likelyto occur. This exerts a detrimental influence upon the slidingproperties of Ni-B plating. Thin Zn plating is also carried out as apre-treatment prior to the application of Ni-B plating. However in thiscase also, the problems as described above occur.

When Ni-B plating is applied on the surface of aluminum-alloy directlyor with an intermediary of the Zn intermediate plating layer, Al or Zndissolves from the work piece into the Ni-B plating liquid and is thenincorporated into the Ni-B plating coating. Al and Zn exert adetrimental influence in the form of impurities and result indecomposition of the plating liquid and hence impairment ofproductivity.

DISCLOSURE OF INVENTION

It is, therefore, an object of the present invention to discouragechipping and peeling of the electroless Ni-B plating coating formed onthe surface of aluminum-alloy, and to provide a sliding material whoseelectroless plating liquid is not detrimentally influenced by thedissolution of components of the mother material.

The sliding material according to the present invention is characterizedby the provision of an electroless Ni-B plating coating formed of thesurface of aluminum alloy via the intermediary of an electroless Ni-Pplating coating.

The Ni-P plating is known itself and is used as the underlying platinglayer in the above referred Japanese Unexamined Patent Publication No.sho 58-193,355 and Japanese Examined Patent Publication No. Hei2-50,933. The present invention is different from the these prior artsin the point that the Ni-P plating is used as an underlying plating forthe purpose of preventing chipping, peeling and the like of theelectroless Ni-B plating coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing the testing apparatus of fatigue resistance.

FIG. 2 is a drawing showing a coated sliding material of the presentinvention.

FIG. 3 is a drawing showing a coated sliding material of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The electroless Ni-P plating is formed by a method known under thecommon name of "Kanigen plating" or the like. The electroless Ni-Pplating liquid sold by Japan Kanigen Co., Ltd., and Uemura IndustriesCo., Ltd., can be used. Heat treatment may be carried out at 200°˜300°C. after carrying out the electroless Ni-P plating. Thickness of theplating coating is preferably from 0.5 to 50 μm, more preferably from 1to 20 μm

The electroless Ni-B plating coating is formed by a known method usingelectroless plating liquid which contains nickel sulfate, amine boraneand the like. The electroless Ni-B plating liquid sold by Dipsole Co.,Ltd., Uemura Industries Co., Ltd., and Okuno Pharmaceutical Co., Ltd.,can be used. Thickness of the electroless Ni-B plating coating ispreferably from 5 to 50 μm, more preferably from 10 to 30 μm.

The substrate, on which these plating coatings are formed, is aluminumor its alloy. For example, a high-Si Al alloy can be used as thealuminum alloy. The surface of such aluminum alloy is polished to adjustthe roughness. Subsequently, a pre-treatment, such as Zn displacementplating 7, may be applied, to the aluminum alloy, followed byapplication of Ni-P plating 8 and the electroless Ni-B plating 9.

The underlying, electroless Ni-P plating coating can prevent theelectroless Ni-B plating coating from peeling and chipping, presumablyfor the following reasons. The electroless Ni-P plating has a hardnessof Hv 400˜500 and amorphous structure. The electroless Ni-P platingcoating is therefore softer than and of a structure different from themicro-crystalline Ni-B coating having a hardness of Hv 700˜900. Inaddition, the Ni-P plating has excellent throwing power. Furthermore,the hardness distribution profile of the coating with an intermediaryNi-P layer is gentle as compared with the Ni-B layer directly applied onthe substrate. Due to these properties, the electroless Ni-P coatingenhances the adherence of the electroless Ni-B plating coating and actsas a buffer layer when impact is imparted. In addition, since the growthspeed of the electroless Ni-P plating is fast as compared with that ofthe electroless Ni-B coating, it is possible to prevent the dissolutionof Zn, Al and the like from the substrate or intermediate layer.

Since the electroless Ni-P plating coating has the properties asdescribed above, it mitigates the load concentration in the electrolessNi-B plating coating and enhances its fatigue resistance. Therefore,fatigue peeling does not occur, allowing the sliding member according tothe present invention to be used stably over a long period. Theelectroless Ni-P plating coating is a barrier metal which prevents theAl dissolution from the aluminum substrate, or the Zn dissolution fromthe Zn plating coating. By this, the productivity is enhanced and thetreatment properties are stabilized.

In addition, the heat treatment carried out after the electroless Ni-Pplating or electroless Ni-B plating renders the Ni-P plating structuremicro-crystalline and hence increases its hardness to approximately Hv700 or more. The heat treatment also enhances the adherence of Ni-Pplating to both the substrate and Ni-B plating coating.

The present invention is hereinafter described further in detail by wayof an example.

BEST MODE FOR CARRYING OUT THE INVENTION

An aluminum-alloy rolled sheet (JIS, ADC12) was subjected to degreasing,etching and Zn displacement plating (Zn displacement liquid produced byOkuno Pharmaceutical Co., Ltd.). The following plating treatment wasthen carried out.

(1) Electroless Ni-B plating (comparative example)

Electroless Ni-B plating liquid (product of Okuno Pharmaceutical Co.,Ltd.) was used to form a 20 μm thick plating coating (hardness Hv700˜900).

(2) Electroless Ni-B plating after electroless Ni-P plating (inventiveexample)

Electroless Ni-P plating liquid (product of Okuno Pharmaceutical Co.,Ltd.) was used to form a 2 μm thick plating coating, and, subsequently,the electroless Ni-B plating coating according to (1) was formed.

(a) Generation of peeling

Each ten coatings for the above coatings (1) and (2) were subjected tothe peeling-property test by the following method. An indenter of aRockwell C harness-tester (radius of curvature of the diamond front tipis 0.2 mm, and the angle of diamond front tip is 120°) was pressedagainst the surface of the plating coating and was moved on the platingsurface in a horizontal direction, while the pressing load in thevertical direction was increased at a rate of 30 kgf/min up to 12 kgf.The moving speed of the indenter was: F_(y) (the speed in horizontaldirection to the surface of the plating coating) =10 mm/min, and, F_(z)(the vertical and downward speed to the surface of plating coating) =15mm/min. As a result of these tests, the following properties wereobserved.

Presence or absence of peeling was investigated when the load to reachedthe maximum. Peeling did not occur for all the coatings of the example(2), while all the coatings of the comparative example (1) peeled.

(b) Adherence strength of the coating

Load in a horizontal direction, at which the peeling generated, wasmeasured to evaluate the adherence.

Inventive Example: 12 kgf or more for all ten coatings

Comparative Example: 6 kgf for all ten coatings

(c) Fatigue resistance

Coating was formed on a vane of a rotary compressor by the methods (1)and (2). For the so prepared samples, the fatigue resistance wasmeasured by the apparatus shown in FIG. 1. In the drawing, 1 is a vane,2 is a fixing bolt, 3 is a rubber vibration-insulator, 4 is quenchedsteel which is the opposing material, 5 is the coating layers. The testwas carried out under the following condition.

Load: minimum zero--maximum 2000 kgf (refer arrow)

Frequency: Hz

Number of times repeated: 5×10⁴, 10×10⁴, 20×10⁴ times

Test results are shown in Table

                  TABLE 1                                                         ______________________________________                                                  Repeating Number of times repeated                                            5 × 10.sup.4                                                                     10 × 10.sup.4                                                                      20 × 10.sup.4                             ______________________________________                                        Comparative Test N=1   Test N=3.  Test N=1                                    Example     No peeling Peeling    Peeling                                     Inventive   Test N=1   Test N=3   Test N=1                                    Example     No peeling No peeling No peeling                                  ______________________________________                                    

As is understood from the above example, the inventive electrolessplating coating does not peel, as opposed to the electroless Ni-Bcoating alone. The inventive electroless plating coating has improvedadherence and fatigue-resistance.

INDUSTRIAL APPLICABILITY

The sliding material provided by the present invention does not peelduring sliding against the opposite material, and, therefore, exhibitsstably excellent wear-resistance of the electroless Ni-B plating.

We claim:
 1. A vane of a compressor, comprising a coated slidingmaterial wherein said coated sliding material comprises: an aluminumalloy, an electroless Ni-P plating coating having a thickness from 0.5to 50 μm provided on the surface thereof and an electroless Ni-B platingcoating provided on the Ni-P plating coating.
 2. The vane of acompressor of claim 1, wherein said electroless Ni-B plating coating hasa thickness of 5 to 50 μm.
 3. The vane of a compressor of claim 2,wherein said electroless Ni-P plating coating has a thickness of 1 to 20μm.
 4. The vane of a compressor of claim 3, wherein said electrolessNi-P plating coating is approximately one tenth the thickness of saidelectroless Ni-B plating coating.
 5. The vane of a compressor of any oneof claims 1-4, wherein said electroless Ni-P plating coating has ahardness of more than 700 Hv.
 6. A vane of a compressor,comprising analuminum alloy a Zn displacement plating applied on the aluminum alloysurface, an electroless Ni-P plating coating having a thickness of 0.5to 50 μm provided on the surface of the Zn displacement coating and anelectroless Ni-B plating coating provided on the surface of saidelectroless Ni-P coating.
 7. The vane of a compressor of claim 6,wherein said electroless Ni-B plating coating has a thickness of 5 to 50μm.
 8. The vane of a compressor of claim 7, wherein said electrolessNi-P plating coating has a thickness of 1 to 20 μm.
 9. The vane of acompressor of claim 8, wherein said electroless Ni-P plating coating isapproximately one tenth the thickness of said electroless Ni-B platingcoating.
 10. The vane of a compressor of any one of claims 6-9, whereinsaid electroless Ni-P plating coating has a hardness of more than 700Hv.